Dummy plug or seal for fuse sockets



June 29, 1937. F. B. THOMSON DUMMY PLUG OR SEAL FOR FUSE SOCKETS Filed Feb. 25, 1955 2 Sheets-Sheet 1 INVENTOR f E EQEE/CKBZOMJQ:

ATTORNEY Patented June 29, 1937 PATENT OFFICE DUMlVIY PLUG R SEAL FOR FUSE SOCKETS Frederick B. Thomson, Teaneck, N. J., assignor to Metropolitan Device Corporation, Brooklyn, N. Y., a corporation of New York Application February 25, 1933, Serial No. 658,652

13 Claims.

This invention relates to dummy plugs to take the place of fuse plugs in a house wiring system and thereby insure against reestablishing a connection with an outside service line when the service has been out ofi. It has for its principal object a self-contained plug construction that is sealed against removal and necessitates the destruction of the seal in order to replace it by the usual fuse plug.

10 y In general, the plug comprises a threaded body to screw intoa fuse plug socket. The body is made of insulating material, such as porcelain, molded synthetic resin composition or other known compositions or materials suitable for the 15 purpose. Rotatably attached to the threaded body is a shell preferably of insulating material to avoid establishing any electrical contacts. The

" shell extends suificiently into the fuse plug socket so that external access cannot be had to the threaded body for unscrewing it when the plug is inv place in the socket. In order to screw or unscrew the threadedbody, the hollow shell gives internal access to a post, for rotating the threaded body orequivalent means are provided. I When 325 the plug is in place, the opening in the shell is closed by-means of a self-locking sealing cap or breaking button. After the sealing cap has been applied, the dummy plug can only be removed by des yin t .In theaccompanying drawings two embodiments of the invention are illustrated. It is to be understood, however, that modifications and changes can be made in conformity with the appended claims.

In the drawings:

Fig. 1 is a vertical cross-section of a dummy plug shown with a sealing cap and in assembled relation with a fuse plug socket;

Figs. 2, 3, 4, 5 and 6 are perspective views of the 0 several parts entering into the construction of the plug shown in Fig. 1;

Fig.;7is a perspective view of an operating tool;

Fig. 8 is a partial cross section similar to Fig. 1

5 but illustrating the operation of the tool for destroying a seal; 7 r Fig. 9 isa top view partly in section of the second embodiment of the invention;

Fig. 10 is a vertical cross section on the line Fig- 11 is a vertical cross section on the line l.-H' of Fig. 9 and further showing the plug in place in a fuse plug socket;

. Fig. 121s a view similar to Fig. 11 but illustrat- 55 ine a ina an PQ Q Fig. 13 is a perspective view of a modified form of sealing cap; and

Figs. 14, 15 and 16 are perspective views of detailed parts entering into the construction of the p ug.

Referring to the embodiment shown in Fig. l a fuse plug socket ll of the usual form is illustrated enclosing a threaded metal shell [2; in the bottom of the socket is a customary central terminal [3. With the usual form of fuse plug a circuit is established between the terminal 13 and the shell 12. The dummy plug of this invention has, however, no metal parts to establish a circuit; therefore when the fuse plug is replaced by it the circuit is broken, and the circuit cannot be closed as long as the dummy plug is in place.

The dummy plug illustrated consists of two sections rotatably connected together. One of these sections is a threaded body [5 which fits in the metal shell I2; this body is made of nonconducting material as heretofore explained but preferably molded from a synthetic resin composition. The threaded body is hollow or cup shaped and encloses a boss i 6 that supports a metal post ll axially of the member 15. The post near its free end is provided with an annular groove l8 and the end 20 of the post is flattened so that it can be engaged by a suitable tool for turning. A locking collar or split ring 19 is provided for engagement with the groove H3.

The other section of the dummy plug consists of a, member 22 preferably molded from a synthetic resin composition which encloses a cup shaped metal shell 2|. The member 22 is provided with a groove 23 in which fits a flange 24 formed on the metal shell 2 I. The molded member also has an outer projecting flange 25 extending over the socket H. There is likewise an inwardly projecting flange 26 formed on the member 22 leaving a central opening 21 to permit access to the post !7. The bottom of the member .22 is formed with a rounded edge so as to have as little frictional contact as possible with the other section I5. The metal shell 2! is centrally perforated to receive the post I! and when the locking collar 19 is snapped in place on the post it engages the bottom of the shell 2| and prevents the separation of the two sections.

The foregoing describes the dummy plug construction as it is supplied to the trade for insertion in a fuse plug socket. Together with the plug there is supplied a seal such as a button or cap 28. U-shaped prongs 29 extend from the disc portion of the button. When the plug is in position in a socket the button 28 is inserted through the opening 2'] and the prongs 29 have sufficient spring to engage the flange 26 and thereby prevent the withdrawal of the button. In other Words the button is self-locking and can only be removed by destroying it. The button is made of metal soft enough so that it can be punctured with a suitable tool and upon withdrawal of the tool the prongs crumple out of shape.

For turning the member 55 into the socket there is provided a suitable tool such as illustrated in Fig. 7. This tool consists of a shank 33 having one end 32 slotted to engage the fiattened end 28 of the post H. An enlarged guide 3% on the shank aids in positioning the tool in the plug. A cross pin 33 is provided for turning the shank. 'The other end of the shank 34 is formed into a gimlet that can be forced through the button 28 and upon turning has suflicient hold upon the button so that it can be withdrawn by pulling the tool. This is illustrated in Fig. 8. Preferably the tool is inserted near one edge of the button so that upon pulling the nearest prong 2Q is crumpled and the button thereby removed.

The second embodiment disclosed difiers from the one previously described in the means provided for rotating the section l5. As shown in Figs. 9 to 12 inclusive, it consists of a threaded body 55 and a molded member 22 in rotatable contact therewith. The member 22 encloses a cup shaped metal shell 2! as in the preceding construction, and a post 35 is embedded axially in the molded member l to project upwardly through an opening (it in the bottom 37 of the shell 2!. A locking collar 38 carried in a groove 39 of the post engages the bottom 3'! of the shell and thereby prevents separation of the two sections. The post 35 is hollow and encloses a spring at. The post is likewise provided with slits M which serve as guides for a latch 42 of inverted T-shape having a shank G5 and wings 43 with upstanding lugs 44 on the ends of the wings. The shank 45 of the latch is formed with an extrusion 46 engaging the interior of the hollow post that thereby serves as a guide.

The metal shell 2! is provided with slots 4'1 in the bottom 31 for engagement by the lugs 44 of the latch 52. The spring 46 mentioned above serves to hold the lugs in engagement with the slots. Consequently with the construction thus far described the two sections l5 and 22 are caused to rotate together by the latch engaging the shell 2i when the member 22 is turned.

For disengaging the latch and holding it disengaged, the sealing button or cap 28 as previously described is inserted in the member 22. This is accomplished by'making the shank 45 of the latch of sufficient length so as to engage the button 28 when the latter is in place and hold the lugs 44 out of engagement with the slots 41.

A modified form of sealing button 28 is shown in Fig. 13. This modification consists in forming the disk portion 48 with lines of weakness or rupture 49. The metal of the button is thereby su liiciently weakened so as to be broken without necessitating the use of a special tool and the button can thereupon be withdrawn. When the button is withdrawn the latch springs into operation locking the sections I 5 and 22 together so that the whole plug rotates by turning the member 22.

I claim:

1. A plug comprising in combination a nonconducting body for insertion in an electrical socket, a cup-shaped shell in axial alignment with said body, a post projecting axially from said body and through an opening in the shell bottom, means for locking the shell against axial movement on the post, a spring pressed latch supported by said post and rotatable therewith, and means on said shell for engagement by said latch.

2. A plug comprising in combination a nonconducting body for insertion in an electrical socket, a cup-shaped shell in axial alignment with said body, a post projecting axially from said body and through an opening in the shell bottom, means for locking the shell against axial movement on the post, and means associated with the post for rotating the body.

3. A plug comprising in combination a nonconducting body for insertion into an electrical socket, a hollow member rotatably connected with said body, means enclosed by said member for turning said body, and a destructible selflocking seal for said member to prevent the operation of said turning means.

4. In a plug comprising in combination two sections rotatably connected together, a latch carried by one of said sections, spring means for causing said latch to engage the other section, anda sealing cap carried by the plug in contact with said latch to prevent engagement of the latch.

5. In a plug comprising in combination two sectionsrotat-ably connected together, means for rotating one of said sections by the other of said sections, and a self-locking cap carried by the other or said sections for preventing the rotation ofrsa id first-named section.

6. In a plug comprising in combination two sections rotatably connected together, means for rotating one of saidsections, and a self-locking cap carried by the other of said sections for barring the rotation of said first-named section.

7. A plug comprising in combination a nonconducting body for insertion into an electrical socket, means carried by said body for turning it, and self-contained means connectively associated with said body for sealing saidturning means against operation.

8. A circuit isolating plug comprising an inner externally screw-threaded insulating section and an outer insulating section that is free from screw-threads, means rotatably connecting said "two sections in axial alignment, said inner section having a polygonalfsection-rotating stem which said outer section overlies and said outer section having a passage leading from said end face to said stem into which passage a suitable tool can be inserted to engage said stem and which is not greater than the root diameter of Y the screw-threads of said inner section, said outer section also having a peripherally outstanding annular shoulder and a dome-shaped end face, said inner section having a section-rotating stem which said outer section overlies and said outer section having a passage leading from its end face to said stem, and means r otatably connecting said sections together and holding said sections in axially aligned relation.

10. A circuitisolating plug comprising an inner externally screw-threaded 'sec'tion and an outer section that'has a rotatable connection with said inner section, said inner section having aforwardly extended stem and-said outer section having a passage therein in which said stem is located,

'said stem constituting the means by which said inner section can be rotated and said stem being polygonal in cross-section and the width of its fiat faces being so small that it inhibits sufficiently firm engagement by a make-shift tool inserted in said passage to rotate said inner section when it is screwed into a socket.

11. A circuit isolating plug comprising an inner externally screw-threaded insulating section and an outer section aligned with and having a freely rotatable connection with said inner section, said inner section having a forwardly extended hub on which said outer section is rotatable and held against detachment and said hub having a forwardly extended axial stem by which said inner section is adapted to be rotated, said outer section having a passage leading from its end face to said stem, and said stem being of non-circular cross-sectional area and being so small in its cross-sectional dimensions that it inhibits sufficiently firm engagement by a make-shift key that can be inserted through said passage in said outer section to cause said inner section to be unscrewed from a socket in which it is seated.

12. A circuit isolating plug comprising an inner externally screw-threaded insulating section, and axially aligned therewith an outer section having a freely rotatable non-detachable connection with said inner section, said inner section having a forwardly projecting axially located stem which said outer section overlies and by which said inner section is adapted to be rotated, said outer section having an axially directed passage leading from its end face to said stem, said stem comprising a rod of metal of polygonal cross-section that is embedded in said inner section and is so small in its cross-sectional dimensions that it inhibits sufilciently firm engagement by a makeshift tool that can be inserted through the passage in said outer section to unscrew said inner section from a socket in which it is seated.

13. A circuit isolating plug comprising axially aligned inner and outer sections, said outer section having a recess and said inner section having external screw-threads and a forwardly-extended axially-disposed hub that is located in said recess, said outer section having means that project into said recess and loosely engage said hub and hold said sections rotatably and against detachment, said hub having a forwardly-extended metal stem of polygonal cross section and small cross-sectional dimensions, and said outer section having a passage for a stem engaging innersection rotating tool that leads from the end face thereof to said stem.

FREDERICK B. THOMSON. 

